A recent study published in Engineering has demonstrated a controllable interfacial redox strategy using electrochemically exfoliated graphene (EG) to tailor the surface chemistry of nickel‐based metals, leading to enhanced electrocatalytic performance for the oxygen evolution reaction (OER). Metallic nickel serves as a common precatalyst that reconstructs into nickel oxyhydroxide (NiOOH) under OER conditions, and the resulting NiOOH phase directly governs catalytic activity and stability. Researchers from Zhejiang University and Dalian University of Technology showed that EG can selectively oxidize nickel foam (NF) surfaces to form favorable Ni²⁺ species that convert into γ‐NiOOH rather than the less active β‐NiOOH phase during anodic polarization.
In situ characterizations revealed that the EG‐mediated redox process suppresses the formation of β‐NiOOH and stabilizes γ‐NiOOH, which contains highly oxidized Ni⁴⁺ sites associated with higher intrinsic OER activity. Single nickel atoms and clusters were anchored onto the EG layers during the reduction step, creating additional active sites while protecting the underlying metallic nickel from excessive oxidation. The modified EG–NF electrode exhibited improved OER metrics, including a lower overpotential at a benchmark current density and a smaller Tafel slope, indicating faster reaction kinetics. Electrochemical impedance measurements confirmed accelerated charge transfer, and the increased electrochemical surface area further contributed to the enhanced performance.
The team verified the versatility of this interfacial redox modulation by adjusting the graphene type and extending the approach to other nickel‐based substrates. When applied to a nickel–iron (NiFe) bimetallic system, the optimized EG–NiFe electrode delivered further improved OER performance. Long‐term durability tests showed stable operation at a high current density over extended hours, supporting potential use in industrial alkaline water electrolyzers. Density functional theory calculations supported the experimental observations, showing that γ‐NiOOH presents more favorable energetics for OER intermediates than β‐NiOOH, with a lower calculated overpotential for the rate‐determining step.
This work provides a controllable pathway to engineer active NiOOH phases and metal single atoms on conductive graphene supports, offering a scalable method to design high-performance OER electrodes for sustainable hydrogen production via water splitting. The findings highlight the importance of interfacial redox chemistry in tuning precatalyst reconstruction and may be extended to other transition metal systems for broader energy conversion applications.
The paper "Superior Electrocatalytic Oxygen Evolution of Nickel-Based Metals Modulated by Controllable Graphene Layers via Interfacial Redox Process," is authored by Zhibin Liu, Dashuai Wang, Xinyi Tan, Libin Zeng, Xianyun Peng, Bin Yang, Zhongjian Li, Lecheng Lei, Yang Hou. Full text of the open access paper: https://doi.org/10.1016/j.eng.2024.04.028
